Herpes simplex virus (HSV) infections are responsible for recurrent corneal herpetic keratitis, as well as sporatic acute encephalitis. Even with antiviral treatment, the incidence of mortality or severe neurological deficits after HSV encephalitis remains high. Our long-term goal is to identify the viral and infected host proteins that promote the spread of HSV into the central nervous system. Using a novel in vivo mouse retinal ganglion cell model, we have found that the HSV viral protein, Us9, is necessary for the long distance spread specifically of viral nucleocapsid and viral DNA from an infected neuron cell body toward the axon terminal. Understanding the mechanisms underlying targeted delivery of virus leads directly to the identification of vulnerable steps in HSV and other neurotropic viral infections, such as CMV and VZV. We now propose to define the regions of the Us9 that are necessary for efficient nucleocapsid sorting. We shall also define the viral proteins and host proteins that associate with Us9 in infected axons. Lastly, we shall test the function of virus and host motor proteins in the delivery of nucleocapsids within an infected axon using a novel, microscale culture system. Understanding the pathophysiology of the virus in mature neurons is important, because the mechanisms of HSV transmission between neurons is essential for development of new antiviral drugs that block viral encephalitic spread. In addition, what we learn about HSV transmission will be relevant for fighting other virus infections. PUBLIC HEALTH RELEVANCE: Herpes simplex type 1 (HSV) and type 2 are responsible for the majority of herpetic encephalitis cases. HSV is also the pathogen responsible for recurrent scarring of the corneal epithelium in ocular herpetic keratitis, a common cause of blindness. HSV can become latent in infected neurons and can become resistant to treatment with acyclovir and acyclovir-derived drugs. Thus, exploration of the mechanisms used by the virus to infect sensory neurons and travel to the central nervous system is of value in that it will provide insight into potential vulnerabilities of the pathogen that can be exploited therapeutically.